(CBS NEWS) -- After a series of bilateral meetings with Afghan President Hamid
Karzai, President Obama today announced the acceleration of the U.S.
military transition in Afghanistan, and said the U.S. military will play
a support role in the nation by this spring.

Mr.
Obama, in a joint press conference with Karzai this afternoon, said
that swift progress on the part of both U.S. and Afghan forces had
enabled both nations to not only meet previously-enumerated goals, but
to "accelerate them somewhat."

"Today we agreed that as
Afghan forces take the lead and as President Karzai announces the final
phase of the transition, coalition forces will move to a support role
this spring," Mr. Obama told reporters. "Our troops will continue to
fight alongside Afghans when needed, but let me say it as plainly as I
can: Starting this spring our troops will have a different mission --
training, advising, assisting Afghan forces. It will be an historic
moment and another step for full Afghan sovereignty."

As the
United States prepares for the official drawdown at the end of 2014,
there has been much speculation as to the size and scope of the U.S.
presence there going forward. Mr. Obama said today that while he and
Karzai discussed their mutual goals for post-2014, he doesn't yet know
how how many U.S. troops -- if any -- will be required in meeting those
goals. He did say that any troop presence would have to be at the
"invitation" of the Afghan government, and that he would demand immunity
for those troops.

"With regard to post-2014, we've got two goals
-- and our main conversation today was establishing a meeting of the
minds in terms of what those goals would be," Mr. Obama said. He
described those goals, which include training, assisting and advising
Afghan forces, and "making sure that we can continue to go after the
remnants of al Qaeda or other affiliates that might threaten our
homeland," as "a very limited mission."

"It is not one that would require the same kind of footprint, obviously, that we've had over the last 10 years in Afghanistan."

Even
as the administration continues preparations for winding down the
10-year war, Mr. Obama reflected today on the nation's extended presence
in Afghanistan, acknowledging that while America's loftiest goals there
had "probably not" been met, the military has "come very close to
achieving" its central goal of dismantling al Qaeda.

"We
went into Afghanistan because 3,000 Americans were viciously murdered by
a terrorist organization that was operating openly and at the
invitation of those who were then ruling Afghanistan," Mr. Obama told
reporters. "Because of the heroic work of our men and women in uniform,
and because of the cooperation and sacrifices of Afghans who had also
been brutalized by that then-host government, we achieved our central
goal, which is -- or have come very close to achieving our central goal
-- which is to de-capacitate al Qaeda, to dismantle them, to make sure
that they can't attack us again."

"It was absolutely the right thing to do," Mr. Obama added, of the decision to go after al Qaeda.